I picked up my lower today and ordered my lpk last night (Daniel Defense...I knew I would be picking up lower today). Well, I got to thinking that I really want to assemble every part on my rifle, so I started looking at Uppers an Stocks and what not. The reason I want to assemble every piece myself, is because I really want to know all the inner workings of my rifle. Mainly because, in case something breaks, then I will know how to disassemble it and repair it.

My dilemma comes in, is this a smart thing to do to completely assemble it myself or should I just buy a completed upper with barrel?

Just put the barrel (with barrel extension on it) into a vise (with padded jaws) and then get your bolt and carrier group. CLEAN THE CHAMBER. Make sure there's no dirt or crap in the chamber - check it with a flashlight.

Put in the go gage. Put the bolt (extended out from the carrier) into the extension. Push forward.

The bolt should rotate closed completely.

Pull the bolt backwards. Pull out of the extension. Pull the go gage out of the chamber, wipe it down and put it back into the container in which it came.

CHECK THE CHAMBER again for dirt, dust, etc. Put in the no-go gage. Extend the bolt from the carrier and push the bolt into the extension again. Now the bolt should NOT rotate to full closure. You can tell this because the carrier will not be all the way up to the back of the extension - it should be sticking off the extension by 1/16th to 1/8th of an inch.

Pull out the bolt, pull out the no-go gage, wipe down and return to container.

You're done.

The only time I've seen this fail is when someone put on their own barrel extension and they did not torque the barrel extension down onto the barrel tenon with a torque wrench or the proper tools - which then allows a bolt to close on a no-go gage.

If you're putting on your own barrel extension, then get a proper extension driver to put into the flutes of the extension, and get a 1/2" drive torque wrench. The spec torque is 150 ft-lbs. Do not skip on this torque. Get your barrel into a proper vise with proper lead soft jaws, or you need to get some aluminum or plastic blocks around your barrel into a vise without soft jaws. If you're using plastic or aluminum blocks to hold your barrel in a vise, you might find that you need some powdered rosin to keep your barrel from slipping as you torque on the extension.

Our Grendel barrel came with a matched bolt, so it was unncecessary for us.

"Technically", as long as the barrel extension/chamber and bolt are within specs, headspacing would be fine, and a lot of guys do barrel changes without verification. Just a different animal...there is no way to adjust headspace anyway- short of removing the barrel extension and machining/re-chambering the barrel. Problems are extremely rare, just make sure to torque the barrel to spec.

You're right - as long as the barrel tenon, the depth of the chamber, the barrel extension and the torque of the extension onto the tenon are within spec... the headspace issue on AR-15's is largely a non-issue.

The only time I become concerned is when people put on their own barrel extensions. That's it, really. And that's because we gunsmiths usually "budget" about .002" for the "crush" of parts when threaded together under torque. On a bolt action rifle, we allow .002" for "crush" when we thread a barrel onto a receiver, and I allow/budget for that same .002" when I thread an extension onto a barrel for the first time and torque it to 150 ft-lbs.

Edit: I'd be spending the extra money on reloading gear. I suspect that if these idiots in Congress can't get what they want on weapons and magazine restrictions, they'll broaden their gaze and start hammering on ammo availability - eg, no more mail order ammo.

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